The interior and exterior trim components of vehicles such as automobiles must have a high strength and excellent appearance properties, and in addition are undergoing weight reduction by reducing thickness and miniaturizing, with the goals, inter alia, of cost reduction and resource savings. Thermoplastic polyester resins such as polybutylene terephthalate resins inherently have excellent mechanical properties, electrical properties, etc. and also an excellent chemical resistance, heat resistance, etc., and are therefore broadly used for a variety of components for vehicles such as automobiles. In addition, so-called fiber-reinforced polyester resins—which are obtained by blending a fibrous reinforcement, e.g., glass fiber, carbon fiber, and so forth, into a thermoplastic polyester resin—exhibit greatly enhanced mechanical properties and for this reason are also used as vehicle components (See PTL 1).
Among vehicle components, for example, lamp-related components, e.g., automotive headlamps and so forth, are components for which mechanical properties and appearance properties are particularly required; this includes the component known as a lamp extension, which is alongside the reflector and has a function of light concentration and reflection (See PTL 2). In order to concentrate and reflect light, the lamp extension has a metal, e.g., aluminum, vapor deposited on a thin-walled—generally about 2 mm—molded article that has a complex reflective structure.
Reinforced resins obtained by the incorporation of an inorganic filler, e.g., talc, mica, and so forth, in a polybutylene terephthalate resin exhibit an excellent heat resistance and appearance and as a result are widely used for these lamp component applications. In particular, the main stream for lamp extensions is to carry out aluminum vapor deposition after the primer treatment on the surface of a molded article of a reinforced polybutylene terephthalate resin. Reinforced polybutylene terephthalate resins generally have microscopic bumps and dents on the surface, and, when aluminum vapor deposition is performed directly on a molded article formed of a reinforced polybutylene terephthalate resin, light is diffusely reflected by these bumps and dents and a satisfactory reflective light-focusing effect is not obtained; as a result, treatment with a primer becomes a necessary step in order to use these molded articles.
However, the primer treatment step is directly connected to an increase of production costs and also limits the design freedom, and a primerless direct vapor deposition is thus desired. In general, smooth-surface unreinforced resins also offer the possibility of omitting the primer treatment, but they produce problems with, for example, the secondary shrinkage behavior, heat resistance, and shrinkage ratio. In particular, complex shapes have come to be required of lamp extensions in recent years, and mold release problems also frequently occur with unreinforced polybutylene terephthalate resins, which have high shrinkage ratios. In addition, unreinforced resins exhibit large shrinkage ratio differences from reinforced resins, and a problem that can also occur in the molding of unreinforced polybutylene terephthalate resin is that the mold used for the reinforced resin cannot be repurposed.
Thus, unreinforced polybutylene terephthalate resin materials present the possibility of direct vapor deposition, but also present the difficulty in handling with lamp extension-related applications that reflect recent trends.
At present, a high flowability is required of the resin composition due to the upsizing of automotive lamp components and a reduction in the number of components, and because of this methods are generally used in which the flowability is secured by raising the resin molding temperature.
However, gases (volatile component) are readily produced during molding with these methods. This volatile component causes the production of fogging-like appearance defects on the surface of the lamp component, and as a result good-quality lamp components cannot be continuously obtained and new countermeasures, e.g., polishing or wiping the mold, then become necessary. Moreover, the surface of the light-reflecting body is fogged due to deteriorating the surface of the metal thin film by exposing to high temperature atmospheres.
Given these circumstances, there is strong demand for a polybutylene terephthalate resin material that adapts direct vapor deposition, that has a low shrinkage ratio and excellent mold release properties and an excellent appearance, and that resists the production of fogging even during use at high temperatures.